The present invention relates generally to wireless telecommunication networks, more specifically, the invention relates to a method of packet system access for migration in an integrated D-AMPS/EDGE wireless telecommunication network.
The evolution of wireless telecommunication systems has led to continuing improvements in quality, capacity, and added functionality as compared to prior generations. One area of added functionality has been the introduction of packet switched data services such as General Packet Radio Service (GPRS) specified for use with the Global System for Mobile Communications (GSM) wireless standard. The implementation of packet switched services in wireless telecommunications allows for the introduction of a number of new data based services in current generation systems, e.g., enhanced support for Internet communications. Packet switched techniques provide a significant improvement in efficiency for utilizing radio resources relative to conventional circuit switched techniques.
Packet switched connections are an especially suitable means for transmitting data (including voice data) over the air interface since radio resources are only reserved when the data or voice data, which are divided into packets, need to be sent. Resources are relinquished and made available to other users during breaks between the packets thereby freeing up radio spectrum during periods of non-use. Further gains in efficiency are achieved by sharing resources among users by having multiple users share the same time slot. In contrast, conventional circuit switched techniques allocate radio resources for the entire time of the transmission. A comprehensive description of GPRS and packet data communications is given in PCT publication WO/9516330 entitled: xe2x80x9cApparatuses and Mobile Stations for Providing Packet Data Communication in Digital TDMA Cellular Systemsxe2x80x9d, published on Jun. 15, 1995 with a priority date of Dec. 10, 1993 and assigned to the present assignee, the disclosure of which is incorporated herein by reference.
An example in the trend toward wireless evolution has been the development of the Enhanced Data Rates for GSM Evolution (EDGE) which is currently under standardization within the European Telecommunication Standards Institute (ETSI). The EDGE specification has also been selected by the Universal Wireless Communications Consortium (UWCC), as the outdoor high speed data component of UWC-136, as a common evolution path for IS-136 Digital Advanced Mobile Phone System (D-AMPS) and GSM to support high-bit-rate wireless data services such as simultaneous voice, internet services, and video at transmission up to speeds of 384 kbps (48 kbps per timeslot). The EDGE specification, using the GPRS backbone as a core network, provide packet data communications based on the current GSM Time Division Multiple Access (TDM) frame structure, logical channel structure and 200 kHz carrier bandwidth. The UWCC selected component for D-AMPS evolution provides support for the seamless transition between the D-AMPS modulated channels (in which the air interface standard provides for 30 kHz carrier bandwidth) and EDGE modulated channels, thus also enabling multi-mode operation comprising both circuit switched and packet switched services.
A UWCC requirement, in compliance with IMT-2000 criterion, designates in the specification for EDGE channels that they are to be deployed for operation within one megahertz (1 MHz) of frequency spectrum. The relatively confined frequency range of 1 MHz necessitates the use of a ⅓ frequency reuse cell plan for effective operation. As known by those skilled in the art, the cell plan is indicative of the frequency reuse distance between cells and wherein the farther the distance, the lesser the probability of experiencing co-channel interference. But a problem resulting from the use of a ⅓ cell plan is that the radio environment is poor i.e. channel link interference levels are too high for the reliable use of common control signaling on the 200 kHz network. Therefore, it becomes extremely difficult to rely solely on 200 kHz common control signaling in this environment to manage mobile station (MS) migration from the 30 kHz packet portion of the network to the 200 kHz GPRS packet portion of the network for packet transfers, for example. Consequently, one method would be to access to access the 30 kHz control channels, in addition to accessing the 200 kHz control channels, in order to facilitate migration.
However, in an integrated D-AMPS/EDGE network, there are some intrinsic incompatibilities that exist between the 30 kHz and 200 kHz networks involving the Medium Access Control (MAC) layer which pose particular problems for the smooth migration between the packet systems. In particular, issues that involve obtaining timing advance and packet transfer identifiers for packet transfers on the first network prior to migration to the second network in order to successfully operate on the second network are particularly problematic.
The MAC layer provides the important function of arbitrating access to the shared medium between a plurality of MSs and the network i.e. it provides mediation between multiple MSs attempting to transmit simultaneously and provides collision avoidance, detection and recovery procedures etc. Timing advance involves the adjustment in the transmissions between the MS and the base station (BS) such that propagation delays are compensated for as the MS moves farther away from the BS. But since timing scales are different between the networks i.e. the length of the time slots on the 30 kHz network and 200 kHz network are different, timing advance acquired on the one network is typically not valid on the other. For packet transmissions, the GPRS packet system requires a Timing Advance Index (TAI), which is obtained when the MS sends an access burst in which the network can derive the correct timing advance. Typically, this can only be obtained from the 200 kHz network in which an MS operating on the D-AMPS network ordinarily does not have access to.
Similarly, the packet transfer identifier i.e. the Active Mobile Identifier (AMI) on the 30 kHz D-AMPS packet portion of the network is generally not compatible with the Temporary Flow Identifier (TFI) used in the GPRS/EDGE packet portion of the network. This is because a packet identifier on one packet system uniquely identifies a specific packet transfer by the network that assigned it. Thus, an AMI assigned on the 30 kHz network D-AMPS packet portion of the network will not be recognized by the to 200 kHz GPRS packet system.
In view of the foregoing, it is an objective of the present invention to provide an access method that provides means for acquiring the information necessary to successfully migrate from the D-AMPS packet portion of the network to migrate to the GPRS/EDGE based packet portion of the network.
Briefly described, and in accordance with an embodiment thereof, the invention discloses a method of migrating a mobile station (MS) camping on or in packet transfer mode on a Digital Advanced Mobile Phone System (D-AMPS) 30 kHz modulated channel to an Enhanced Data Rates for GSM Evolution (EDGE) 200 kHz modulated channel. In accordance with an embodiment of the invention, the method includes an access sequence performed by the MS in two steps. In a first access step, the MS accesses the 30 kHz D-AMPS control channel, and if it is determined that a migration to the 200 kHz EDGE/GPRS packet system is necessary, the MS acquires information directing the it to a radio block reserved on the 200 kHz EDGE control channel. The radio block specifies a specific frequency and timeslot for said access by the MS. In the second access step, the MS accesses the EDGE control channel as specified by the acquired reserved block wherein thereon the MS sends a series of shortened access bursts to the network. The network uses the shortened bursts to estimate a Timing Advance Index (TAI) that is transmitted back to the MS together with a Temporary Flow Identity (TFI) that is assigned to the packet transfer. Furthermore, the network then assigns a packet data channel for use by the MS in packet mode in preparation for a packet transfer.
The present invention describes a technique for migrating a multi-mode MS camping on or in packet transfer mode on a D-AMPS modulated channel to the General Packet Radio Service (GPRS) network operating on an EDGE modulated channel. The two-step access, occurring first on the D-AMPS control channel and then on the EDGE control channel, provides a solution to the problem of obtaining the necessary information for GPRS packet transfers, i.e. associated timing advance and packet identifier of the transfer. These and other advantages of the present invention will become apparent upon reading the following detailed description and studying the various figures of the drawings.